1. Field of the Invention
The present invention relates to a water-soluble polymeric adhesion promoter and methods for its production. In particular, the present invention relates to a water-soluble polymeric adhesion promoter useful for oxidizable metals such as copper, and to methods for its production.
2. Description of the known art
Numerous polymers have been used to provide coatings and adhesiveness to metals, including alkyd, acrylic, epoxy, polyester and polyurethane resins. These polymers are required to bond well to the metals and to provide good coverage, in order to provide corrosion resistance and adhesiveness to the metals.
For this purpose, JP 4-80277A proposes adhesive resins containing a benzotriazole ring in the molecule. The resins may be polyesters, polyurethanes or polyacrylic polymers. However, the benzotriazole ring-containing resin of JP 4-80277A is resistant against solvents and water, and furthermore, is required to be water-insoluble for use in metal coating technologies. The benzotriazole ring is linked directly to the polymer chain.
On the other hand, the use of copper has expanded in the semiconductor fabrication industry due to its excellent electrical and thermal properties. Copper is highly oxidizable and its oxides have a fragile structure, and thus problems remain to be solved in terms of the processability and reliability of the semiconductor fabrication process. The conventional adhesion promoters or corrosion inhibitors employed for metals or ceramics are not suitable for copper or copper products, for example lead frames made from copper (xe2x80x9ccopper lead framesxe2x80x9d), because copper is highly oxidizable and the copper oxides have a weak structure.
Azole compounds or polybenzimidazole (PBI) have been used to inhibit corrosion of, and provide adhesiveness to, copper metals, in particular copper lead frames. Azole compounds including benzotriazole (BAT) are advantageously used because they are water-soluble. However, they have the disadvantages of poor coverage and poor adhesiveness.
Even though polybenzimidazole (PBI) is advantageous over azole compounds in terms of coverage and adhesiveness, it still has the problem that it is not soluble in water and thus requires expensive solvents such as dimethylacetamide (DMA). Moreover, DMA causes environmental pollution.
Thus, there has been a need to provide an aqueous adhesion promoter which can provide, when it is applied to an oxidizable metal, good coverage on the metal surface and excellent adhesiveness for bonding to other materials.
The present invention provides a new aqueous polymeric adhesion promoter which does not have the problems associated with conventional adhesion promoters or corrosion inhibitors such as benzotriazole ring-containing polymers, azole compounds or polybenzimidazoles. The present invention provides a new polymer useful in inhibiting the corrosion of oxidizable metals and in providing good adhesiveness to the metals for bonding to other materials.
In accordance with one aspect of the present invention, there is provided a polymer represented by the following formula (I): 
wherein
R is a hydrogen atom, a hydroxyl group or a lower alkyl group having 1 to 4 carbon atoms, and
m and k are numbers selected such that m/k is in the range from about 1/0.001 to about 1/0.1, and such that that the polymer (I) has a weight average molecular weight of about 3,000 to about 600,000.
In particular embodiments, m and k are numbers selected such that the polymer (I) has a molecular weight of about 30,000 to about 100,000.
The present invention also provides a method for the production of the polymer of the formula (I) that includes the step of reacting N-(4-phenolyl)-(benzotriazole)amide of the formula 
with a polyacryloyl chloride comprising units of the formula 
wherein n=m+k.
The present invention also provides an adhesion promoter composition for treating oxidizable metals, which comprises the polymer of the formula (I) and an aqueous carrier.
The present invention further provides a method for treating the surface of an oxidizable metal which comprises the step of applying the polymer of the formula (I) to the surface of the oxidizable metal to provide anti-corrosion and adhesiveness. In particular embodiments, the polymer is applied in the form of an aqueous solution.
The above and other features of the present invention will be apparent to those skilled in the art from the detailed description given below.
Priority Korean Patent Application No. 2000-51487, filed Sep. 1, 2000, is incorporated herein in its entirety by reference.
The aqueous polymeric adhesion promoter according to the present invention is represented by the following formula (I) 
wherein
R is a hydrogen atom, a hydroxyl group or a lower alkyl group having 1 to 4 carbon atoms, and
m and k are numbers selected such that m/k is in the range from about 1/0.001 to about 1/0.1, and such that that the polymer (I) has a weight average molecular weight of about 3,000 to about 600,000.
The polymer (I) provides good coverage, good corrosion inhibition and excellent adhesiveness when applied to the surface of oxidizable metals.
The polymer (I) can be prepared by following the process indicated in the reaction scheme (1) given below. 
wherein
n=m+k, and
R, m, k and mr/k have the same meanings as defined above in relation with formula (I).
The polymer (I) can be prepared as follows. Thus, 4-aminophenol ({circle around (1)}), benzotriazole-5-carboxylic acid (xe2x80x9cCBTAxe2x80x9d {circle around (2)}) and triphenyl phosphate (xe2x80x9cTPPxe2x80x9d {circle around (3)}) are reacted together to give N-(4-phenolyl)-(benzotriazole-5-carboxyl)amide (xe2x80x9cPBCAxe2x80x9d {circle around (4)}) and diphenyl phosphate ({circle around (5)}). The reaction may be carried out by heating the reaction mixture to about 60-160xc2x0 C. in the presence of base in an organic solvent.
The base can include, but is not limited to, pyridine, ammonia, Rxe2x80x23N (wherein Rxe2x80x2 includes lower alkyl groups having 1-3 carbon atoms) and the like.
The organic solvents can include, but are not limited to, N-methyl pyrrolidone (NMP), dimethyl formamide and the like. TPP ({circle around (3)}) is used in the same or almost equivalent amount as aminophenol ({circle around (1)}), and the organic solvent is used in an excessive amount, for example about 3 times the amount of aminophenol ({circle around (1)}). 
Then, a polyacryloyl chloride including units having the formula xe2x80x94[CH2xe2x80x94C(R)COClxe2x80x94]nxe2x80x94 is reacted with PBCA ({circle around (4)}) to obtain the desired polymer, poly(acrylic-co-4-(5-benzotriazole)amidophenyl acrylate) (PAB, (1)). This reaction can be carried out by heating the reaction mixture to about 20 to about 160xc2x0 C. in the presence of base in an organic solvent.
The base can include, but is not limited to, pyridine, ammonia, Rxe2x80x23N (wherein Rxe2x80x2 includes lower alkyl groups having 1-3 carbon atoms) and the like.
The organic solvents can include, but are not limited to, N-methyl pyrrolidone, dimethyl formamide and the like.
The equivalent ratio of acryloyl chloride in polyacryloyl chloride to PBCA is determined depending on the desired value of m/k. Thus, the equivalent ratio is the same as the value of m/k.
For the present invention, the weight average molecular weight of the polymer (I) preferably is about 3,000 to about 600,000 and more preferably about 30,000 to about 100,000, and is determined by the values of m and k. The ratio of m/k preferably is about 1/0.001 to about 1/0.1. If the m/k ratio is higher than about 1/0.001, the relative content of azole moiety in the polymer (I) is low and the resulting polymer (I) cannot provide satisfactory adhesiveness. If the m/k ratio is lower than about 1/0.1, the polymer (I) is hardly soluble in an aqueous medium, resulting in a limitation of use.
The ratio between the acid group and the benzotriazole group in the polymer is important to give proper water-solubility to the polymer (I) and to provide good adhesiveness to the oxidizable metals. The ratio preferably is between about 1/0.1 and about 1/0.001. In particular, when a metal such as copper is treated with a polymer according to the invention wherein the ratio of m/k is about 1/0.003, the metal shows an increase in adhesiveness of about 4 times.
When a composition containing the polymer (I) is applied to the surface of oxidizable metals, it gives a good coverage of the metals and the metals show good adhesiveness. The metals can be treated by applying the composition by way of dipping the metals in an aqueous solution of the composition or spraying the solution on to the metals. That is to say, the polymer (I) is dissolved in water or a water-alcohol mixture in an amount of about 0.05 to about 1 wt % to give an aqueous solution of the polymer (I). Then, the metals to be treated are dipped into the aqueous solution at a temperature of about 20 to about 80xc2x0 C., rinsed with water or a water-alcohol mixture and then dried at about 20 to about 150xc2x0 C. Alternatively, the aqueous solution of the polymer (I) is sprayed onto the metals for about 1 to about 10 seconds and then rinsed and dried similarly.
No additive is required to prepare the aqueous solution of the polymer (I). However, surfactants may be used to increase the solubility of the polymer (I).
The metals to be treated by using the polymer (I) of the present invention include, but are not limited to, oxidizable metals, in particular copper metals. Particularly, lead frames for semiconductor fabrication process can advantageously be treated with the polymer (I). If the lead frames made from oxidizable metals are treated with the polymer (I) they can keep good adhesiveness and are resistant to corrosion during several reliability tests under severe and strict conditions of the semiconductor fabrication process. The lead frames can be made from, but are not limited to, copper metals such as Cuxe2x80x94Fe alloy, Cuxe2x80x94Cr alloy, Cuxe2x80x94Nixe2x80x94Si alloy or Cuxe2x80x94Sn alloy.
The present invention will be illustrated by way of working examples, which should not be construed as limiting in any way the scope and sprit of the invention.